A transistor-based biosensor including a transistor is one of apparatuses for detecting biomolecules using an electrical signal. The transistor-based biosensor, which is fabricated through a semiconductor process, has such an advantageous merit as rapid switching of an electrical signal, and thus many studies are being conducted on the transistor-based biosensor.
In particular, an apparatus (or biosensor) for detecting biomolecules using a field effect transistor (FET) requires low cost and short time, and is compatible with IC/MEMS process easily.
In a biosensor using a FET, target molecules (or analyst molecules, analytes) bind to probe molecules (or receptor molecules, acceptors) in a channel region or a gate of the FET, so that the amount of current flowing through the channel region varies due to a variation in a surface charge transferred to the channel region of the FET. This is used to detect the target molecules.
The intensity of a current flowing through the channel region may vary because the Debye length of a surface charge varies according to an ionic strength of a solution, that is, ion concentration. Therefore, target molecules can be detected using the FET under condition that the ionic strength of an electrolyte solution containing the target molecules is smaller than a charge quantity of the target molecule.
Meanwhile, body fluids including biomolecules, e.g., blood, serum, plasma, urine, or saliva, have different ion concentration for each person, and have relatively high ionic strength. Therefore, it is difficult to detect biomolecules by providing the biomolecules to the channel region of the FET directly. Moreover, even though the biomolecules are detected by measuring the current intensity of the channel region, the reliability and re-producibility become poor. Consequently, a buffer solution, which maintains the ion concentration constantly, is required to detect the biomolecules. Alternatively, body fluids containing the biomolecules should be diluted to detect the biomolecules. That is, typical apparatuses for detecting biomolecules using a FET can detect the biomolecules only if the solution has a low ionic strength.